全文获取类型
收费全文 | 625篇 |
免费 | 56篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 21篇 |
大气科学 | 101篇 |
地球物理 | 152篇 |
地质学 | 204篇 |
海洋学 | 47篇 |
天文学 | 102篇 |
综合类 | 1篇 |
自然地理 | 66篇 |
出版年
2022年 | 5篇 |
2021年 | 22篇 |
2020年 | 19篇 |
2019年 | 16篇 |
2018年 | 20篇 |
2017年 | 26篇 |
2016年 | 54篇 |
2015年 | 31篇 |
2014年 | 30篇 |
2013年 | 46篇 |
2012年 | 52篇 |
2011年 | 38篇 |
2010年 | 42篇 |
2009年 | 52篇 |
2008年 | 34篇 |
2007年 | 30篇 |
2006年 | 35篇 |
2005年 | 26篇 |
2004年 | 20篇 |
2003年 | 14篇 |
2002年 | 7篇 |
2001年 | 14篇 |
2000年 | 13篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有694条查询结果,搜索用时 93 毫秒
631.
632.
633.
A computer correlation technique was used to deduce the spreading history of the Mid-Atlantic Ridge from 5 magnetic profiles between 28°S and 43°S. In general, several possible histories are indicated for each profile involving changes of spreading rate and faulting, some of which are easily overlooked by the visual method. The only spreading history that was consistent will all the profiles required spreading at approximately 2.2 cm yr-1 from 11 m.y.b.p. to approximately 5.5 m.y.b.p., followed by a decrease in rate to 1.7 cm yr-1 relative to the Vine (1966) magnetic reversal model based on the South Pacific. Comparison of the data with other reported spreading rate discontinuities suggests that the South Pacific may be reponsible for the reported spreading rate changes. 相似文献
634.
Translating ecosystem indicators into decision criteria 总被引:3,自引:1,他引:3
635.
Solute-based geochemical mass balance methods are commonly used in small-watershed studies to estimate rates of a variety of geochemical processes at the Earth’s surface, including primary-mineral weathering and soil formation, and the quantitative contribution of these elemental transfer processes to cation budgets, nutrient cycling, and landscape susceptibility to acid deposition. Weathering rates of individual minerals in watershed mass-balance studies are determined by solving a system of simultaneous linear geochemical mass-balance equations with constant (stoichiometric) coefficients. These equations relate the measured net fluxes to the (known) stoichiometries and (unknown) rates of weathering reactions for multiple minerals in the weathering profiles. Solving the system of equations requires petrologic, mineralogic, hydrologic, botanical, and aqueous geochemical data. The number of mineral-weathering rates that can be determined is limited by the number of elements for which solute mass-balance equations can be written. In addition to calculating mineral weathering rates, elemental transfer into or out of the biomass may also be calculated. Elemental uptake by aggrading forest vegetation can act as an intrawatershed sink for at least some mineral-derived cations, producing mineral weathering rates higher than would be estimated from solute fluxes alone; similarly, element release from decaying forest biomass can result in higher solute fluxes than are produced by weathering alone. The mathematics of, significant contributions from, role of biomass in, and recent advances in, watershed geochemical mass-balance methods are discussed using examples from the Appalachian headwaters watersheds of the Coweeta Hydrologic Laboratory in the southern Blue Ridge Physiographic Province of North Carolina, USA. 相似文献
636.
Cave sediments collected from Reflection Cave on the Vaca Plateau, Belize show variations in the δ13C values of their fulvic acids (FAs), which indicate periods of vegetation change caused by climatic and Maya influences during the late Holocene. The δ13C values range from − 27.11‰ to − 21.52‰, a shift of ∼ 5.59‰, which suggests fluctuating contributions of C3 and C4 plants throughout the last 2.5 ka, with C4 plant input reflecting periods of Maya agriculture. Maya activity in the study area occurred at different intensities from ∼ 2600 cal yr BP until ∼ 1500 cal yr BP, after which agricultural practices waned as the Maya depopulated the area. These changes in plant assemblages were in response to changes in available water resources, with increased aridity leading to the eventual abandonment of agricultural areas. The Ix Chel archaeological site, located in the study area, is a highland site that would have been among the first agricultural settlements to be affected during periods of aridity. During these periods, minimal water resources would have been available in this highly karstified, well-drained area, and supplemental groundwater extraction would have been difficult due to the extreme depth of the water table. 相似文献
637.
Countries can use both mitigation and adaptation strategies to protect their citizens from catastrophic risk posed by climate
change (e.g., shift in the jet stream). A nation can mitigate by reducing CO2 emissions, which reduces the probability of a catastrophic event; it can adapt by altering the infrastructure so that damages
can be reduced in the event a catastrophe is realized. Herein we add to the current literature by extending the endogenous
risk framework into a dynamic framework permitting analysis of both mitigation and adaptation while allowing for the dynamic
process of global climate change. Our results suggest adaptation to catastrophe is a small fraction of the national climate
protection budget relative to mitigation when nations cooperate fully, when damages are both continuous and catastrophic,
and when nations have a short planning horizon. Adaptation becomes more important relative to mitigation when nations are
unlikely to cooperate, when damages are mainly catastrophic, or when the nation’s planning horizon increases. 相似文献
638.
639.
The present study describes a procedure for quantitatively analyzing satellite telemetry data to identify interspecific land use differences among four threatened crane species. The inherent inaccuracy of satellite telemetry data points, the temporal autocorrelation of those points, and the resolution of two land‐cover imagery products from the IGBP‐DISCover Global Land‐Cover Characterization Project (derived from AVHRR data) were assessed and integrated in a GIS. Satellite telemetry is a system where animals are tracked using battery‐operated transmitters and locations are calculated using triangulation from satellites. Using the variable spatial inaccuracy of the telemetry locations, each point was buffered using a radius based on the accuracy of the point, and then intersected with the land cover imagery. The research concluded that the methodology is valuable for studies of birds at a regional scale, with interspecific differences clearly evident, but that diurnal and nocturnal differences were not discernable due to the coarse resolution of both satellite telemetry and land‐cover data. 相似文献
640.
Jason Ronald Janke 《Geografiska Annaler: Series A, Physical Geography》2005,87(4):515-526
Flow rates for rock glaciers in the European Alps have been monitored using photogrammetric techniques; however, a program has not been initiated for similar Front Range, USA, rock glaciers. Horizontal rock glacier displacements were measured by tracking large surficial rocks on temporal orthophotos from 1978, 1990, and 1999. Vertical change was measured by creating digital elevation models (DEMs) from digital stereopairs, then subtracting elevations to detect change. Long‐term horizontal velocities ranged from 14 to 20 cm/yr on average, although uncertainty ranged from 4 to 5 cm/yr. On average, vertical elevation changes were negligible with most rock glaciers exhibiting a slight growth or thinning (1–2 cm/yr). Over shorter time scales (c. 10‐year periods), horizontal velocities have only increased by about 2 cm/yr. Because horizontal and vertical change is minimal, Front Range rock glaciers appear to be adjusted with current climate, unlike some rock glaciers in the European Alps that have shown increasing subsidence rates or significant increasing or decreasing horizontal velocities. 相似文献